Production of magnesium from magnesiferous raw materials by thermal reduction



Patented Dec. 28, 1937 UNITED STATES PATENT OFFICE PRODUCTION OFMAGNESIUM FROM MAG- NESIFEROUS RAW MATERIALS BY THER- MAL REDUCTIONration of Delaware No Drawing. Application November 12, 1936, Se-

i'iqaala No. 110,482. In Germany September 23,

5 Claims.

The present invention relates to improvements in the production ofmagnesium from magnesiferous raw materials by thermal reduction,particularly with the aid of silicon as a reducing agent.

In processes for the thermal reduction of magnesiferous raw materialssuch as magnesite or dolomite with the aid of silicon, at temperaturesbelow the melting point of the reaction residue, be it under atmosphericor only moderately reduced pressure in an atmosphere of hydrogen, orunder a high vacuum, and particularly when the reaction mixture isemployed in the form of brlquetted moulded bodies, it has been observedthat the speed of the reaction does not remain uniform, but diminishesprogressively as the reaction proceeds. Even an increase of thetemperature of the reaction mixture during the later stages of thereaction does not result in an appreciable acceleration while at thesame time involving the risk that parts of the reaction mixture and/orof the residue may become heated above theirmelting temperature, whichis undesirable.

It has now been ascertained that an addition to the reaction mixture ofthe fluorides of the alkali and alkaline earth metals in comparativelysmall proportions leads to a substantial acceleration of the reactionvelocity, particularly in the later stages of the reaction. The lowestproportion of the addition of fluoride or fluorides, with which anappreciable effect is obtained, is about 0.5 per cent. by weight of theoriginal reactionmixture; on the other hand an addition exceeding 5 percent. by weight of the reaction mixture should be avoided since suchaddition would again result in impairing the reaction. Whilst beneficialresults are thus obtained by additions ranging between about 0.5 and 5per cent. by weight of the reaction mixture, it has been found that themost preferable proportion of fluorides to be added is about 2 per cent.of the original reaction mixture.

The most favorable results are obtained by the addition of cryolitheNOaAIFs. the alkali metals, NaF and KF, and the fluorides of thealkaline earth metals, particularly CaFz and MgFz, also exercise afavourable influence,

" and the use of CaF: is moreover indicated because ing made inconjunction with the employment of reaction mixtures in the form ofbriquetted moulded bodies, and particularly when such bodies contain forevery 4 mols of bases (MgO or MgO-l-CaO) not more than 1 mol. ofsilicon, has the efiect of reducing the reaction residue which, in thelatter case, substantially consists of dicalcium silicate, topulverulent form, whereas, in the absence of fluorides, these residues,on cooling, assume the form of more or less coarse compact lumps. Thefact that it is thus possible to obtain the reaction residues inpulverulent form throughout is obviously of particular convenience indealing with their discharge from the furnace, particularly when suchdischarge is to be effected from a furnace operated under reducedpressure by means of a double-valve device.

Example sisting of 87.5 per cent. by weight of dolomite and 12.5 percent. by weight of ferrosilicon (93% Si) was subjected to a temperatureof 1350 C. Chemical analysis of the reaction residue which was Withdrawnfrom the furnace in the form of coarse lumps, showed that, after a giventime, 75 per cent. of the silicon employed had reacted. The same mixturehaving been briquetted after addition of 2 per cent. of calcium fluoridewell admixed therewith, other conditions of operation, and particularlythe speed of conveyance through the furnace, remaining unchanged, showedthat, on the average, 95 per cent. of the silicon had reacted, and theresidue, as discharged from the furnace, was of a purely pulverulentnature.

We claim:

1. A process for producing magnesium by thermal reduction ofmagnesiferous compounds by means of silicon, which comprisesincorporating in the reaction mixture at least one substance of thegroup consisting of alkali, alkaline earth metal, and aluminum fluoridesin quantities ranging between about 0.5 to about 5 per cent by weight ofsuch reaction mixture, the reaction mixture being such as to yield anexclusively solid residue at the reaction temperature, and subjectingthe reaction mixture thus treated to temperatures adapted to causevolatilization of the magnesium.

2. A process for producing magnesium by thermal reduction ofmagnesiferous compounds by means of silicon, which comprisesincorporating in the reaction mixture at least one substance of thegroup consisting of alkali, alkaline earth metal, and aluminum fluoridesin quantities of approximately 2 per cent by weight of such reabout 5per cent by weight of cryolithe, said reaction mixture being such as toyield an exclusively solid residue at the reaction temperature, andsubjecting the reaction mixture thus treated 5 action mixture, thereaction mixture being such to temperatures adapted to causevolatllization 5 as to yield an exclusively solid residue at the of themagnesium. reaction temperature, and subjecting the re- 5. A process forproducing magnesium by the!- action mixture thus treated to temperaturesmal reduction of magnesiferous compounds by adapted to causevolatilization oi the magnesium. means of silicon, which comprisesincorporating l0 3. A process for producing magnesium by therin areaction mixture containing for every tour 10 mal reduction ofmagnesiferous. compounds by molecules of MgO or MgO+CaO not more thanmeans of silicon, which comprises incorporating one molecule of silicon,at least one substance in the reaction mixture between about 0.5 to ofthe group consisting of alkali, alkaline earth about 5 per cent byweight of calcium fluoride, metal, and aluminum fluorides in quantitiesrang- 15 said reaction mixture being such as to yield an ing betweenabout 0.5 to about 5 per cent by 5 exclusively solid residue at thereaction temperaweight of such reaction mixture, said reaction ture, andsubjecting the reaction mixture thus mixture being such as to yield anexclusively treated to temperatures adapted to cause volasolid residueat the reaction temperature, and tilization oi the magnesium. subjectingthe reaction mixture thus treated to 20 4. Aprocess for producingmagnesium by thertemperatures adapted to cause volatilization of 20 malreduction of magnesiierous compounds by means of silicon, whichcomprises incorporating in the reaction mixture between about 0.5 to

the magnesium.

. ROBERT SUCHY.

HELLMU'I'H SELIGER.

CERTIFICATE OF CORRECTION.

Patent No. 2,103 ,9 76.

December 28, 1957.

ROBERT SUCHY', ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 15, in the formula, fox-"we ring" read NaAlF g; andthat'the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 22nd day of February, A. 1). 9-58.

Henry Van Arsdale,

' (Seal) Acting Commissioner of Patents.

in the reaction mixture at least one substance of the group consistingof alkali, alkaline earth metal, and aluminum fluorides in quantities ofapproximately 2 per cent by weight of such reabout 5 per cent by weightof cryolithe, said reaction mixture being such as to yield anexclusively solid residue at the reaction temperature, and subjectingthe reaction mixture thus treated 5 action mixture, the reaction mixturebeing such to temperatures adapted to cause volatllization 5 as to yieldan exclusively solid residue at the of the magnesium. reactiontemperature, and subjecting the re- 5. A process for producing magnesiumby the!- action mixture thus treated to temperatures mal reduction ofmagnesiferous compounds by adapted to cause volatilization oi themagnesium. means of silicon, which comprises incorporating l0 3. Aprocess for producing magnesium by therin a reaction mixture containingfor every tour 10 mal reduction of magnesiferous. compounds by moleculesof MgO or MgO+CaO not more than means of silicon, which comprisesincorporating one molecule of silicon, at least one substance in thereaction mixture between about 0.5 to of the group consisting of alkali,alkaline earth about 5 per cent by weight of calcium fluoride, metal,and aluminum fluorides in quantities rang- 15 said reaction mixturebeing such as to yield an ing between about 0.5 to about 5 per cent by 5exclusively solid residue at the reaction temperaweight of such reactionmixture, said reaction ture, and subjecting the reaction mixture thusmixture being such as to yield an exclusively treated to temperaturesadapted to cause volasolid residue at the reaction temperature, andtilization oi the magnesium. subjecting the reaction mixture thustreated to 20 4. Aprocess for producing magnesium by thertemperaturesadapted to cause volatilization of 20 mal reduction of magnesiierouscompounds by means of silicon, which comprises incorporating in thereaction mixture between about 0.5 to

the magnesium.

. ROBERT SUCHY.

HELLMU'I'H SELIGER.

CERTIFICATE OF CORRECTION.

Patent No. 2,103 ,9 76.

December 28, 1957.

ROBERT SUCHY', ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 15, in the formula, fox-"we ring" read NaAlF g; andthat'the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 22nd day of February, A. 1). 9-58.

Henry Van Arsdale,

' (Seal) Acting Commissioner of Patents.

